The invention relates to the use of inorganic or organic polyacids for the treatment of inorganic fertilizers.
In particular, the invention relates to the use of polyacids as a mixture with at least one nitrification inhibitor for the treatment of inorganic fertilizers, the use of selected pyrazole derivatives as nitrification inhibitor in inorganic fertilizers, and as stabilizers of liquid manure or liquid fertilizer formulations, and the corresponding treated inorganic fertilizers per se. Moreover, the present invention relates to pyrazole derivatives which can be used as nitrification inhibitors in inorganic fertilizers, and as stabilizers of liquid manure or liquid fertilizer formulations.
In order to make available to plants in agriculture the nitrogen needed by them, ammonium compounds are mainly employed as fertilizers.
Ammonium compounds are converted microbially to nitrates in the soil in a relatively short time (nitrification). Nitrates, however, can be washed out of the soil. The portion washed out is in this case no longer available for plant nutrition, so that for this reason rapid nitrification is undesirable. For better utilization of the fertilizer, nitrification inhibitors are therefore added to the fertilizer. A known group of nitrification inhibitors are pyrazole compounds.
A problem in the use of pyrazole compounds as nitrification inhibitors is their high volatility. During the storage of fertilizer preparations containing pyrazole compounds, a continuous loss of active compound occurs due to evaporation. The pyrazole compounds must therefore be formulated in a nonvolatile form by means of suitable measures.
To fix the pyrazole compounds, these were converted, for example, into transition metal complexes such as zinc complexes. This is described, for example, in U.S. Pat. No. 4,522,642. The volatility of the active compounds can thus be reduced. For environmental protection reasons, the widespread application of zinc, copper or manganese to the soil is, however, undesirable. Complexes of alkali metals or alkaline earth metals which are environmentally tolerable, are not adequately stable, however, and hydrolyze in the aqueous environment.
It has furthermore been attempted by neutralization of the pyrazole compounds with mineral acids, such as phosphoric acid or hydrochloric acid, to decrease their volatility. DE-A-4 128 828 describes the use of nitrates and phosphates of 3-methylpyrazole for the coating of fertilizers. U.S. Pat. No. 3,635,690 also describes the stabilization of pyrazole derivatives by mineral acids, such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid. These acidic salts of the pyrazole compounds, however, are increasingly susceptible to hydrolysis and for this reason cannot be employed for all applications.
DE-A-4 128 828 further describes the sealing of the coated fertilizer with wax or oil. In the case of hygroscopic active compound salts, however, this process does not lead to a satisfactory resistance to hydrolysis.
Formulations of pyrazoles with polymeric auxiliaries have furthermore been employed. Thus DE 260 486 describes formulations of pyrazoles in urea-formaldehyde condensates. The incorporation of the active compounds into the polymer matrix, however, suppresses the mobility of the active compounds in the soil. In this application form, therefore, the finely divided formulation and fertilizer must be thoroughly mixed with the soil to be fertilized. Otherwise the nitrification inhibitor remains on the surface of the earth with the polymer matrix. The need to mix formulation, fertilizer and soil, however, is laborious.
It is an object of the present invention to provide inorganic fertilizers which contain a nitrification inhibitor whose content does not significantly change during storage and application of the fertilizer, and which remains in the ground after application of the fertilizer and can display its action there. Furthermore, new nitrification inhibitors shall be provided.
We have found that this object is achieved by use of inorganic or organic polyacids for the treatment of inorganic fertilizers. In this case, the treated inorganic fertilizer contains a nitrification inhibitor which is present in the inorganic fertilizer or on its surface. The nitrification inhibitor can furthermore also be employed as a mixture with the polyacid and then passes into this during the treatment of the inorganic fertilizer employed according to the invention, preferably onto the surface thereof.
The use of inorganic or organic polyacids for the treatment of inorganic fertilizers which contain nitrification inhibitors leads to an improved fixation of the nitrification inhibitors in the inorganic fertilizer. The volatility of the nitrification inhibitor is greatly reduced in this case, so that the storage stability of the treated inorganic fertilizer increases. Loss of nitrification inhibitor during a storage period or on application to the soil is avoided.
In addition, the treatment according to the invention and the treated inorganic fertilizer thus obtained have the advantage of ecological acceptability. They contain no toxic substances, such as, for example, zinc, copper or manganese, which in relatively large amounts very severely restrict environmental tolerability and can lead to soil contamination.
The treatment according to the invention can furthermore be carried out in a cost-efficient and ecologically tolerable manner. As a result of the treatment according to the invention, the amount of nitrification inhibitors in the inorganic fertilizer can be reduced because of the decreased volatility, which leads to decreased costs and to a better environmental tolerability of the fertilizers according to the invention. The object is furthermore achieved by the use of compounds of the general formula 
where the radical R1 is a hydrogen atom, a halogen atom or a C1-4-alkyl radical, the radical R2 is a C1-4-alkyl radical and the radical R3 is H or a radical xe2x80x94CH2OH, where if R3 is H the salt of the compounds with phosphoric acid can also be employed, as nitrification inhibitors. Preferably the compound used is 3,4-dimethyl pyrazole, 4-chloro-3-methylpyrazole or a phosphoric acid addition solt thereof.
Polyacids
According to the invention, inorganic or organic polyacids are used for the treatment of the inorganic fertilizers.
In this case, all suitable inorganic or organic polyacids can be used which decrease the tendency of nitrification inhibitors to evaporate.
Inorganic polyacids which can be used according to the invention are isopolyacids or heteropolyacids, in particular polyphosphoric acids or polycyclic acids. The polyphosphoric acids, for example, have the general formula Hn+2PnO3n+1, n being an integer of at least 2, preferably at least 10.
Further inorganic polyacids which can be used are known to the person skilled in the art.
Suitable organic polyacids are those polymers which have a plurality of free carboxylic acid groups. These can be homo- or copolymers. Suitable monomers containing carboxyl groups or carboxylic acid groups are, in particular, monoethylenically unsaturated mono- or dicarboxylic acids having from 3 to 6 C atoms or their corresponding anhydrides, such as, for example, acrylic acid, methacrylic acid, ethylacrylic acid, allylacetic acid, crotonic acid, vinylacetic acid, maleic acid, itaconic acid, mesaconic acid, fumaric acid, citraconic acid, methylenemalonic acid, as well as their esters, such as, for example, monoalkyl maleates, and mixtures thereof. In the case of monoalkyl dicarboxylates, the number of C atoms specified relates to the dicarboxylic acid structure, the alkyl group in the ester radical, independently thereof, can have from 1 to 20 C atoms, in particular from 1 to 8 C atoms. Suitable appropriate monoethylenically unsaturated dicarboxylic anhydrides are maleic anhydride, itaconic anhydride, citraconic anhydride and mixtures thereof. Acrylic acid, methacrylic acid, maleic acid, itaconic acid and maleic anhydride are preferably employed. Acrylic acid is particularly preferably employed.
These monomers containing carboxyl groups or containing carboxylic acid groups can be homopolymerized or copolymerized with further vinylic monomers, such as, for example, C1-8-, preferably C1-4-alkylenes, in particular ethylene or propylene.
The organic polyacid particularly preferably used is polyacrylic acid or polymethacrylic acid.
The inorganic or organic polyacids can be employed as free acids or as partially neutralized ammonium, alkali metal or alkaline earth metal salts thereof. They are preferably employed as free acids.
Polyphosphoric acid and poly(meth)acrylic acid are particularly preferred.
The mean molecular weight of the organic polyacids is preferably from 10,000 to 500,000, particularly preferably from 10,000 to 100,000, in particular from 30,000 to 70,000.
Processes for the preparation of the polyacids are known to the person skilled in the art.
Nitrification Inhibitors
Any desired suitable nitrification inhibitors can be employed in the inorganic fertilizers according to the invention.
The polyacids used according to the invention are particularly advantageously employed for the treatment of inorganic fertilizers which contain these volatile nitrification inhibitors, in particular pyrazole compounds. xe2x80x9cPyrazole compoundsxe2x80x9d is understood as meaning all pyrazole compounds which have a nitrification-inhibiting action, such as are also described, for example, in the publications U.S. Pat. Nos. 3,635,690, 4,522,642 and DE-A-4 128 8-28 mentioned at the beginning in the discussion of the prior art, whose contents with respect to the pyrazole compounds described there are hereby included.
According to one embodiment, the pyrazole compounds used as nitrification inhibitors are those of the general formula below 
where the radicals R1, R2 and R3 independently of one another are halogen atoms, nitro groups, hydrogen atoms or C1-20-, preferably C1-4-alkyl radicals, C3-8-cycloalkyl radicals, C5-20-aryl radicals or alkylaryl radicals, where the last-mentioned 4 radicals can be monosubstituted or trisubstituted by halogen atoms and/or hydroxyl groups.
The radical R1 is preferably a hydrogen atom, a halogen atom or a C1-C4-alkyl radical, the radical R2 is a C1-4-alkyl radical and the radical R3 is a hydrogen atom or a radical xe2x80x94CH2OH.
According to a further embodiment of the invention, the radical R1 in the above formula is a halogen atom or C1-4-alkyl radical, the radical R2 is a C1-4-alkyl radical and the radical R3 is a hydrogen atom or a radical xe2x80x94CH2CH2COOH or xe2x80x94CH2CH(CH3)COOH.
The pyrazole compounds can be employed in the basic form, and also in the form of acid addition salts with inorganic mineral acids and organic acids. Examples of inorganic mineral acids are hydrochloric acid, phosphoric acid, sulfuric acid, preferably phosphoric acid. Examples of organic acids are formic acid, acetic acid, and also fatty acids. Examples of these salts are the hydrochlorides and phosphoric acid addition salts.
The pyrazole compounds can be employed on their own or in the form of mixtures.
Particularly preferred pyrazole compounds are 3,4-dimethylpyrazole, 4-chloro-3-methylpyrazole, N-hydroxymethyl-3,4-dimethylpyrazole, N-hydroxymethyl-4-chloro-3-methylpyrazole as well as the phosphoric acid addition salts of 3,4-dimethylpyrazole and 4-chloro-3-methylpyrazole as well as the hydrochloride of 3,4-dimethyl-pyrazole.
By use of the acid addition salts of the pyrazole compounds, the volatility of the compounds can be further reduced. Thus acid addition salts of the pyrazole compounds are advantageously employed in combination with the treatment according to the invention.
Halogen atoms employed in the above compounds are fluorine, chlorine, bromine or iodine, preferably fluorine, chlorine or bromine.
The preparation of the pyrazole compounds used according to the invention is known. It is described, for example, in EP-A-0 474 037, DE-A 3 840 342 and EP-A-0 467 707. For preparation of the N-hydroxymethylpyrazoles, the corresponding pyrazoles are reacted with formalin solution in methanol. Excess solvent is then evaporated, the compounds being obtained as solids. For the preparation of 3,4-dimethylpyrazole reference is made to Noyce et al., Jour. of Org. Chem. 20, 1955, 1681 to 1682.
The acid addition salts of the pyrazole compounds are obtained by reaction of the pyrazoles with an equivalent of appropriate acid. The preparation of the hydrochloride of 4-chloro-3-methyl-pyrazol is described in Hxc3xcttel et al., Liebigs Ann. Chem. 1956, 598, 186, 194.
Treated Inorganic Fertilizers
According to the invention, inorganic fertilizers are employed. These are ammonium- or urea-containing fertilizers. Examples of ammonium-containing fertilizers of this type are NPK fertilizers, calcium ammonium nitrate, ammonium sulfate nitrate, ammonium sulfate or ammonium phosphate.
The treated inorganic fertilizer according to the invention can be present in powder form or in granule form.
The inorganic fertilizers treated according to the invention contains at least one nitrification inhibitor and is treated with at least one inorganic or organic polyacid. In this case, the inorganic fertilizer can be present as a mixture with the nitrification inhibitor. The nitrification inhibitor can also be present on the surface of the inorganic fertilizer and can then be treated with the polyacid according to the invention. Preferably, the nitrification inhibitor can be applied to the inorganic fertilizer as a mixture with the polyacid to be used according to the invention.
Preferably, the inorganic fertilizer contains as nitrification inhibitor a pyrazole compound or an acid salt thereof. Preferably, the inorganic fertilizer is treated with poly(meth)acrylic acid or polyphosphoric acid.
Preferably, the inorganic fertilizer contains from 0.01 to 1.5% by weight of nitrification inhibitor and from 0.01 to 1.5% by weight of polyacid, based on the treated inorganic fertilizer.
The present invention furthermore relates to inorganic fertilizers comprising a compound of the above general formula, as is defined above, and a treated inorganic fertilizer comprising the abovementioned inorganic fertilizer, which is treated with at least one inorganic or organic polyacid or a mixture of at least one nitrification inhibitor and at least one inorganic or organic polyacid.
Preparation of the Treated Inorganic Fertilizers
The treated inorganic fertilizers according to the invention are prepared by treating the inorganic fertilizer with the polyacid. Preferably, they are prepared by treating the surface of the inorganic fertilizer with the polyacid.
In this case, the nitrification inhibitor can be present as a mixture with the inorganic fertilizer or can have been applied to the inorganic fertilizer before the polyacid. According to one embodiment of the invention, the inorganic fertilizer is treated with polyacid and nitrification inhibitor as a mixture.
In this case, the inorganic fertilizers are treated, e.g. impregnated or sprayed, with the polyacid, the nitrification inhibitor or mixture thereof by spraying them with a liquid preparation, e.g. a solution or suspension of the polyacid, of the nitrification inhibitor or of the mixture and, if desired, drying again. An appropriate process is described, for example in DE-A-4 128 828.
Preferably, nitrification inhibitor and polyacid are applied, e.g. sprayed, onto the inorganic fertilizer in the form of a liquid preparation, e.g. of a solution or suspension of the polyacid, and, if desired, then dried.
In this case, a mixture is preferably employed of from 30 to 98% by weight of at least one polyacid and from 2 to 70% by weight of at least one nitrification inhibitor in a liquid medium, preferably water. The nitrification inhibitor can in this case again be present as an acid addition salt.
The invention also relates to the use of compounds of the general formula 
where
the radical R1 is a hydrogen atom, a halogen atom or a C1-4-alkyl radical,
the radical R2 is a C1-4-alkyl radical and the radical R3 is H or a radical xe2x80x94CH2OH, where if R3 is H, the salt of the compounds with phosphoric acid can also be employed, as nitrification inhibitors.
Halogen atoms employed in the above compounds are fluorine, chlorine, bromine or iodine, preferably fluorine, chlorine or bromine.
Particularly preferred pyrazole compounds are 3,4-dimethylpyrazole, 4-chloro-3-methylpyrazole, N-hydroxymethyl-3,4-dimethylpyrazole, N-hydroxymethyl-4-chloro-3-methylpyrazole, as well as the phosphoric acid addition salts of 3,4-dimethylpyrazole and 4-chloro-3-methylpyrazole. N-Hydroxymethyl-3,4-dimethylpyrazole and N-hydroxymethyl-3,4-chloro-3-methylpyrazole are particularly preferred.
The present invention furthermore relates to a fertilization process, in which treated inorganic fertilizer, as defined in the context of the present application, is applied to the arable soil.
According to one embodiment of the present invention the nitrification inhibitors or inorganic fertilizers as described above are not used for treating soils which are used for corn, cotton, wheat, rice, barley and/or sugar-beet cultures or for treating the respective cultures.
The compounds of the above general formula can furthermore be used for the stabilization of liquid manure or liquid fertilizer formulations, such as, for example, ammonium nitrate-urea solutions or liquid ammonia.
The invention furthermore relates to N-hydroxymethyl-4-chloro-3-methylpyrazole, as well as the phosphoric acid addition salts of 3,4-dimethylpyrazole and 4-chloro-3-methylpyrazole per se, the hydrochloride of 3,4-dimethylpyrazole as well as mixtures of two or more thereof, which, of course, can also be used as nitrification inhibitors, preferably together with the polyacids used according to the invention.
The invention is further described below by means of examples.